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Care Guide

About Care Guides[x] These care guides are written to help your clients understand common conditions, tests, and procedures, as well as to provide basic information about pet care. They are based on the most up-to-date, documented information, recommendations, and guidelines available in the United States at the time of writing. Pharmaceutical product licensing, availability, and usage recommendations are based on US product information. Use the Download Handout button to generate a PDF for printing or e-mailing to your clients.

Hyperthyroidism and Your Cat

    • Hyperthyroidism occurs when a cat’s thyroid gland (an organ located at the front of the neck) produces excess amounts of thyroid hormone.
    • Hyperthyroidism tends to affect middle-aged and older cats.
    • Hyperthyroidism causes the heart to pump faster, which can lead to other problems such as high blood pressure and heart disease.
    • In some cats with hyperthyroidism, the thyroid gland becomes noticeably enlarged.
    • There are three ways to treat hyperthyroidism: medication, surgery, or radiation therapy.
    • Because the exact cause of hyperthyroidism is unknown, it is difficult to determine what measures to take to avoid it.

    What Is Hyperthyroidism?

    If your older cat starts losing a lot of weight despite having a ravenous appetite, the problem might be hyperthyroidism. Hyperthyroidism occurs when a cat’s thyroid gland (an organ located at the front of the neck) produces excess amounts of thyroid hormone. The problem is usually caused by a benign (noncancerous) tumor on the thyroid gland, although a small percentage of thyroid gland tumors in cats can be malignant (cancerous).

    Hyperthyroidism tends to affect middle-aged and older cats. Thyroid hormones play an important role in controlling the body’s metabolism, so most cats with hyperthyroidism tend to burn up energy too rapidly and lose weight despite having an increased appetite. Increased thirst and urination are also associated with this disease. Hyperthyroidism causes the heart to pump faster, which can lead to other problems such as high blood pressure and heart disease.

    What Are the Typical Signs of Hyperthyroidism?

    The typical signs of hyperthyroidism include the following:

    • Weight loss, usually despite an increased appetite (although some cats have a decreased appetite)
    • Restlessness or hyperactivity
    • Diarrhea and/or vomiting
    • Increased thirst and urination
    • Irritability or nervousness
    • Unkempt hair coat
    • Lethargy (tiredness) or weakness

    How Is Hyperthyroidism Diagnosed?

    In some cats with hyperthyroidism, the thyroid gland becomes noticeably enlarged. During physical examination, your veterinarian may be able to feel an enlarged thyroid gland, which can feel like a small bulge on the front of your cat’s neck. After performing a thorough physical examination, your veterinarian will likely recommend blood tests to check for elevated levels of thyroid hormone.

    If hyperthyroidism is diagnosed, your veterinarian may need to run additional tests to further evaluate your cat’s health status and better predict which treatment is most appropriate. These tests might include:

    • Additional blood work
    • Urinalysis
    • Radiographs (x-rays)
    • Electrocardiogram (ECG)
    • Ultrasound examination of the heart
    • Check of your cat’s blood pressure

    What Are the Treatment Options for Hyperthyroidism?

    There are three ways to treat hyperthyroidism: medication, surgery, or radiation therapy. Medication prevents the thyroid from overproducing thyroid hormone but does not cure the condition. Medication must therefore be given for the rest of the cat’s life in order to keep the disease under control. Periodic blood testing to check thyroid hormone levels is also recommended for the duration of therapy.   

    Surgical removal of the affected thyroid gland is another course of treatment. If your cat is healthy enough to undergo anesthesia and surgery, this option can offer a more permanent solution to hyperthyroidism.

    Radioactive iodine therapy involves giving your cat an injection that destroys the diseased thyroid tissue without harming other organs. Because of the regulations associated with handling radioactive materials, this treatment is not available at all practices. This type of therapy can also be expensive and may require a week of hospitalization.

    Your veterinarian will evaluate your cat and recommend the most appropriate treatment option.

    Is Hyperthyroidism Preventable?

    Because the exact cause of hyperthyroidism is unknown, it is difficult to determine what measures to take to avoid it. Regular physical examinations and wellness blood work that includes screening for increases in thyroid hormone levels are recommended to help make an early diagnosis and initiate prompt treatment.